The invention relates to an inspection module for inspecting optical parts for defects.
Series-produced optical parts, for example contact lenses, have to be inspected for defects such as scratches, voids or broken edges. For that purpose it is known to illuminate the optical parts in transmitted light and observe them by means of an image-resolving sensor. Defects, which result in a refraction or scattering of the light, then appear dark. The image data provided by the image-resolving sensor are evaluated by image-processing means. The parts identified as being defective are subsequently rejected.
The problem is that the parts are obtained in production in rapid succession. An inspection module must therefore allow a high throughput. Known inspection apparatuses are relatively slow, and therefore the throughput is severely limited. Furthermore, known inspection apparatuses are of complicated construction.
The problem underlying the invention is to construct an inspection module of the kind mentioned at the beginning, using simple means, in such a manner that a high throughput of optical parts to be inspected is made possible.
The invention is to provide an inspection module which can be used in inspecting of optical parts for defects in a high throughput manner. Other objects, advantages, and features of the present invention will become apparent after review of the descriptions hereinafter and the Claims.
For inspection, the parts to be inspected, for example contact lenses, are introduced into a transport vessel which is filled with liquid, since they are in a stress-free state when in liquid. The test specimen sinks in the transport vessel softly to the bottom. The vessel can be of such a shape that the part adopts a substantially defined position on the bottom. According to the invention, when the transport vessels pass through the inspection station they are closed by transparent lids the inside of whichxe2x80x94at least in the region of the inspection light beamxe2x80x94is wetted by the liquid. Since illumination takes place through the transparent lid, wetting of the lid ensures that variations in the surface of the liquid, such as, for example, waves caused by the movement of the transport vessels, which can impair the measurement, do not occur. That construction of the transport vessels makes it possible for the optical inspection of a contact lens to be carried out directly in the transport vessel and obviates the need for separate process steps. Owing to the simultaneous transport of the contact lenses in the transport vessels and inspection of the contact lenses inside the vessels, a rapid throughput of contact lenses to be inspected is made possible, and efficient and economical inspection is ensured. Since the transport vessels are closed by a lid during the inspection, external influences such as the wave motion of the liquid can be excluded and reproducible measurement is made possible with every vessel in the line. After being inspected, the inspected optical part is taken out of the liquid again and transported away as xe2x80x9cgoodxe2x80x9d or xe2x80x9cdefectivexe2x80x9d. According to the invention, the vessel is conveyed through the inspection station along an endless line, thus making it possible to guide each vessel simply and inexpensively. Since a handling means furthermore runs synchronously with each vessel, a sufficient period of time is available for each individual handling step, so that, despite a high throughput, reliable inspection of the contact lenses is achieved.
Altogether, an inspection module that is simple in construction and in terms of guidance is provided by the invention, since the transport vessels are themselves already equipped with optical properties for the inspection of the optical parts and the expenditure for guiding the individual transport vessels is minimised by arranging them along an endless line.
The vessels can be constructed prismatically with a bottom consisting of transparent material and can be closable by the transparent lid at their open end. The vessels are then illuminated at the inspection station from the lid end and are observed by means of the sensor through the bottom. The prismatic shape of the vessels which is adapted to the dimensions of the optical parts to be inspected ensures that the parts to be inspected sink in the liquid to the bottom in a defined manner and adopt there a defined position.
The optical part to be inspected lying on the inside of the bottom is imaged onto the image-resolving sensor by imaging optical means having a range of sharpness that covers the optical part to be inspected. The thickness of the bottom and the distance between bottom and lid are selected to be sufficiently large that the lid in the same way as the outside of the bottom lies outside the range of sharpness of the imaging optical means. The lid and the outside of the bottom may themselves bear scratches or the like owing to handling of the vessels. Those surfaces, however, are outside the range of sharpness of the imaging of the optical part onto the sensor. Scratches, dust or other defects on the lid or the outside are therefore not xe2x80x9cseenxe2x80x9d sharply by the sensor and cannot produce an illusion of defects in the optical part to be inspected.
When the optical part to be inspected is introduced into the liquid, bubbles which would produce an illusion of defects in the optical part to be inspected may become attached to the part. In an advantageous development of the invention, the inspection module has means for removing bubbles from the liquid before the measurement. The bubble-removing means may operate, for example, with ultrasound.
In a preferred embodiment of the inspection module according to the invention, the endless line is formed by a chain of vessels that is passed around a first and a second turntable having parallel axes of rotation extending at a distance from each other. First handling means for introducing the optical parts to be inspected and for carrying out the inspection revolve with the first turntable, and second handling means for taking out the inspected optical parts revolve with the second turntable. The first handling means can comprise a gripper for placing a lid on the vessel after introduction of the optical part to be inspected and for removing the lid after the inspection. The second handling means can comprise a gripper that, in an entry region of the second turntable, is immersible in the liquid and grasps the optical part and that, in an exit region of the second turntable, is movable out of the liquid together with the optical part. Between the entry region and the exit region of the second turntable, a liquid-exchange region can be provided in which the liquid is removed from the vessels by suction and replaced by new liquid. Conveying means for supplying parts to be inspected and for removing inspected parts, which means run at right angles to the direction of movement of the chain of vessels, can be arranged between the turntables. The handling means can be guided along the endless line by fixed cams past which the handling means run. The liquid-filled vessels can be driven continuously. Cam guidance of that kind is simple to implement. The toothing of the individual vessels provides a fixed coupling, so that altogether the expenditure on guidance is minimised.
Furthermore, the first handling means simply revolve with the first turntable, and the second handling means with the second. Separate synchronisation is therefore unnecessary. Even when the chain of vessels and the turntables are running relatively quickly to obtain a high throughput, there is sufficient time for the various functions of the handling means. The handling means therefore need to move only relatively slowly. That makes it possible to guide the handling means, for example the lifting of grippers, simply by means of fixed cams past which the handling means run together with the chain of vessels. Owing to the simultaneous running of the handling means, driving of the chain of vessels also can be carried out continuously at a constant speed, that is to say not step-wise. That too results in a simplification.
Altogether, the inspection modules constructed in that manner are comparatively small, simple and inexpensive. It is therefore possible to construct an inspection apparatus for inspecting optical parts for defects, especially contact lenses manufactured as injection-moulded parts, in such a manner that a plurality of inspection modules of the above-mentioned kind are each connected by a respective computer to a common server. If one inspection module fails, the entire inspection capacity is not then lost, which would necessarily lead to a stop in production, but a high percentage, for example 80%, of the inspection capacity is maintained.